Conductor.



J. B. SPEED.

CONDUCTOR.

APPLICATION FILED MAY n. 1918.

Patented J an. 28, 1919.

UNITED STATES PATENT OFFICE.

JAMES BUGKNER SPEED, OF NEW YORK, N. Y., ASSIGNOR 'IO WESTERN ELECTRTC COM- PANY, INCORPORATED, OF NEW YORKyN. Y., A CORPORATION OF NEW CONDUCTOR.

Application filed May 11, 1918.

This invention relates to electrical conductors and particularly to conductors for currents of extremely high frequency, such, for instance, as are used in radiotelegraphy.

As is well known, when alternating or pulsating current traverses a conductor of homogeneous cross-section, the variations of the magnetic lines of force are greatest near the center of the conductor, and electrometive forces are thereby generated which give rise to local or eddy currents which tend to force the main current to seek the outer layers of the conductor, thus reducing its effective cross-section and consequently increasing its ohmic resistance. The magnitude of this skinelfect, as it is known, varies with the frequency of the main current and the cross-sectional area of the conductor, although the proportionality factor is such that the resulting transmission losses may frequently be disregarded, yet, these transmission losses must be taken into consideration in the case of operation with high frequency currents such as are employed in radiotelegraphy, or with conductors of considerable cross-section. In order to decrease the skin effect under such circumstances, it has been proposed to use tubular or flat conductors, or conductors having corrugated surfaces or stranded conductors in contact or separated by thin layers of insulation. But while a tubular conductor, for instance, provides a greater conducting area that is at or near the surface of the conductor than does a solid conductor and thus increases the effective cross-section of the metal for high frequency currents, the space occupied by the conductor is substantially increased.

It is the object of the present invention to provide a conductor for high frequency alternating or pulsating currents in which the skin effect is substantially reduced without the necessity of correspondingly increasing the cross-section of the conductor by the inclusion of non-conductin g areas or otherwise departing from the cylindrical type of con- Specification of Letters Patent.

Patented J an. 28, 1919.

Serial No; 233,910.

ductor. Other objects of the invention will appear from the following detailed description.

A preferred embodiment of the invention is shown in the single figure of the accompanying drawing, and comprises a sheath or body 1 of relatively high resistivity in which are embedded a plurality of highly conductive elements 2. The filaments 2 are preferably of copper or similar low resistance material, while the material of the body 1 may be brass or lead or a suitable ductile alloy such as nichrome or other nickel alloy. Each of the filaments 2 is continuous along the conductor, but is laterally separated from the adjacent filaments by the material of the body 1. The filaments 2 thus afford a plurality of low resistance paths, each of small cross-section and spaced from its neighbors, and therefore individually subject, even at high frequencies, to but small transmission loss because of the skin effect. In addition to the large aggregate path afforded to the current by the filaments 2, the body 1 provides a. path which, though of high specific resistance, is of sufficient crosssection to carry a considerable portion of the current. The total resistance along the conductor is therefore small.

On the other hand, the composite conductor is of relatively high transverse resistance. This resistance is due to a greater or less extent to three factors: these are: first. and probably least, the proportionately high resistance offered by the portion of the body 1 between two adjacent filaments 2; second, the film resistance between the contacting surfaces of the filaments 2 and the body 1; third, the thermo-electric, back electromotive forces set up across the junctions of the dissimilar materials of the filaments 2 and the body 1. Although on account of the complications resulting from the difi'erent conductivities of the body 1 and the filaments 2 and the different extents to which they react to high frequency currents, the actual current distribution will vary under different circumstances, yet the transverse resistance above referred to results in substantially lessening the degree to which useful current is forced to the outer layers of the conductor by reason of the retarding effect of eddy currents within the conductor.

The arrangement described above also reduces transverse currents that mayq be set up in the conductor when it is so coiled that the rapidly alternating external field cuts the turns obliquely.

A composite conductor of the kind above described may be made by boring a number of holes in a cylinder of the selected high resistance alloy or metal, parallel to its axis and drawing through these holes tightly fitting wires of high conductivity and then drawing out the whole until it becomes a Wire of the desired diameter.

Another and preferred method is to form a composite ingot in the following manner: A suitable number of highly conductive wires, each about one tenth inch in diameter are mounted so as to be spaced hexagonalwise approximately fifteen hundredths of an inch from center to center; a cylinder of suitable metal or alloy slightly more fusible than the material of the wires is then cast around and between the group of wires; and after the mass has hardened it is reduced to the desired diameter. The individual wires or filaments 2 as well as the composite conductor are shown as circular in cross-section but other shapes may be employed iii desired; and the number of the filaments and their relative positions, as Well as the material of the filaments and of the body 1, may also be varied.

Although the use of the above described composite conductor for the high frequency currents of radiotelegraphy is specifically referred to, it is to be understood that the invention is not limited to that field of use.

What is claimed is:

1. A composite electrical conductor comprising a plurality of spaced highly conductive filaments and a metallic sheath of relatively low conductivity surrounding said filaments and filling the spaces between them.

2. A composite drawn conductor comprising a plurality of spaced conductive filaments and a metallic sheath of lower conductivity surrounding each of said filaments and filling the spaces between them.

In witness whereof, I hereunto subscribe my name this 8th day of May, A. D. 1918.

JAMES BUOKNER SPEED Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents. Washington, D. 0. 

